[mcpherv]

Hi Guys,

I'm replacing electrolytic caps in my 1031, and I've run into a couple caps on various boards that are electrolytic, but seem to be non-polar. They have a funny symbol underneath them on the circuit board, which gives no indication as to polarity (as far as I can tell) and don't have a negative strip indicator on one side of the caps. Please see the attached image for the symbol. Can anyone help me and tell me how I could replace them with polar caps? I know I can arrange two polars back to back to create a non polar, but would it matter which polarity was faceing the two ends of the circuit (ie. the +ves facing the outeside vs the -ves facing outside)? Any help would be greatly apprecated. Thanks,

Vic


Edit: I just found a BP marking on the cap, and I went and looked at digikey, and found bi-polar electrolytic caps. I'm guessing that that is what this is. If anyone can confirm, that would be great. Also, I looked at the circuit diagram, and there is +ve voltage around there, so I would assume that the +ves should be facing outwards, correct?


Edit 2: I would be putting two tantalum caps back to back (yes I know that oscons are better, but they a lot more expensiv than I bought these for), so the esr issue wouldn't be a significant problem, right? Again, any input would be great. Thanks

 

[Larry Fine]

Correct about the non-polarized electrolytics. For no great reason, I would the +'s together, but I'd wait for Tim, Mike, or someone else to respond on the wisdom of using a non-p cap.

 

[mcpherv]

Thanks for the reply. By the way, by putting two of the tants I have back to back, I'd have roughly the same capacitance as the original (I'd have 30mfd instead of the original 33). I would doubt that would pose a problem, correct? Thanks for the input,

Vic

 

[Larry Fine]

No. Most caps have a larger tolerance of error than that (10%).

 

[mcpherv]

I just realized that I might be wrong as to the combined capacitance, and looked it up. I'd actually have a total of 7.5, not 30.... Hmmm. So, I guess the question is whether I should try to just stick two in parallel to get the correct capacitance and hope that the polarity of the tants doen't make funny things happen, or to buy a few non polar electrolytics for here. The thing is that tans have a much lower esr though... Any input from the experts?

 

[gravymaker]

Hey Vic,


I ran into the same thing when recapping my 1031. I did about 40 caps but avoided the ones with that symbol because I didn't know how to proceed.


Sorry that I can't help you, but hopefully the experts can help us!

 

[Guy Kuo]

I'd be a little concerned about reverse biasing the tantalums. If I recall correctly, they have a limited ability to withstand reverse voltage, about 1/10 that of their rating for forward bias. Loading with reverse polarity may lead to the capacitor going bang. I'd get some real non-polarized units for those locations.

 

[kal]

Are the special caps in the signal path by chance? That would help prove that they're bi-polar (since the signal path has AC components).


Why not replace the caps with correct value non-polarized caps? This would be the right thing to do...


I went through my BG800 about a year ago and replaced a good portion of the caps, including a bunch of the bipolar's that were in the signal path on the RGB input board...


Kal

 

[mcpherv]

The caps are directly in the signal path as the r, g, b, and sync signals enter through the connector at the projector. They are the first components that the signal encounters, and must be bi-polar caps, as we all agree on. The reason I don't want to replace them with bipolar electrolytics is because from all the reading I've done in the archives, KBK attempted to minimize esr in the signal path. Electrolytic caps traditionally have much worse esr characteristics than tants do, and will therefore adversley affect the resulting image (especially considering that they directly influence the entire picture where they are located) when compared with the tants.


Since they are the first things that the signal encounters, wouldn't that suggest that the voltages they would be seeing are the standard 0.7volts from the video card? The tants I have are 20 volt, so that would be less than half of the reverse bias spec quoted here. The next question would be whether or not the reverse bias would significantly decrease the life of the tant. And finally, would that power be constantly switching in a traditional ac style, or would there just be some reverse bias at startup and shutdown, so as to limit the damage?


If people think I'm stupid to try it, then maybe I'll get some non-polar tants. Anyone know where I can get some relatively cheaply? I've looked on ebay, but no luck. Thanks,

Vic

 

[Brian Hampton]

Hey,


It's interesting to read about people "recapping" a projector and it makes sense to me to and I may want to undertake it on my 1271 since I've "re-tubed" it and "re-faned" it. How does one go about doing this? I would imagine there are maybe 1000 capacitors in my 1271 but maybe I'm wrong. Do people begin with certain boards like the neck boards, input boards, or convergence boards?


I don't have any good electronics stores near me (in New Hampshire in case you know of one that I don't) and I would have to order stuff from catalogs.


-Brian

 

[mcpherv]

Brian,

Electrolytic capacitors go bad after a few thousand hours of use, and even when just sitting around. Replacing these wth new ones is a good way to mprove the image quality coming from the projector. However, you want to try and get good quality caps (like the panasonic eb and fc caps, or even better are the os-cons for the low voltage stuff)to use as replacments. Many people have modded their imput boards and crt neckboards to start with, and have unanimously deceided that there is a rather large improvment. If you want some good reading on this subject, search the archive for ecp mods. I've spent a good 15 or more hours researching all of this.

Vic